The effects are strongest while you are listening to the tones because your brainwaves are synchronized and tuned into the frequency range you desire at that time.  After you've stopped listening the effects can still linger for a while afterwards.  The timescale will vary from person to person and be affected by what you do after you've stopped listening.
However, those with ASD are sometimes also diagnosed with ADHD. Although they are different conditions, some of the symptoms can be intertwined, which it appears may be the case with your grandson. So I would start by trying out my tracks for ADHD. You can try those out for free on my YouTube channel and I’ve put them together in a playlist here: https://www.youtube.com/watch?v=RKao2oZZPnw&list=PLveg0IEcZWN5iVmMduR9UjLzX_YgCetds. The corresponding MP3 versions for those tracks can be found on my site here: https://www.mindamend.com/intelligence-and-brain-power/. I hope that helps.
Limiting your cash withdrawals to once a week is a quick, easy way to monitor your spending habits. Multiple trips to the ATM make it harder to track your money. If you put yourself on an allowance and pay cash for everything, you're more aware of what you're spending and more careful about what you buy. And while thinking about your finances may be enough to send you over the edge, it turns out that getting them under control eases tension in the long run. (Money and work tied for first place as the leading sources of stress, according to an APA survey.) When you have a weekend afternoon free, try this take-control move: Write everything down, so you can see exactly where you stand financially--what you owe, the amount of interest, your monthly income, your budget. Not facing what you're up against creates even more stress, because it's always in the back of your mind. But once you have the information down, you can begin setting concrete goals using real figures. And taking action will make you feel so much better.
Dealing with sudden stress—a phone call with bad news, a last-minute assignment from your boss, or an argument with your spouse—triggers a cascade of physical and mental symptoms that can be hard to stop. The first thing to do? Pay attention to your breathing pattern, and make an effort to start taking slow, deep breaths as stress relievers. “Breathing can change how we feel because emotions and breathing are closely connected,” says Emma Seppala, PhD, author of The Happiness Track and a Stanford University psychologist who’s done research on yogic breathing. “A revealing research study showed that different emotional states are associated with distinct respiration patterns.” In a follow-up study, participants actually started to feel the emotions that corresponded to an assigned breathing pattern. “This finding is revolutionary: We can change how we feel using our breath!” Dr. Seppala says. Deep breathing gets more oxygen to your brain and may lower levels of the stress hormone cortisol.

John Dupuy is the CEO of iAwake Technologies and travels internationally to teach and inspire on the subjects of Integral Recovery, Integral Transformative Practice, and the use of brainwave entrainment technology to deepen one’s meditation practice and in the treatment of addiction, depression, and PTSD. John is the founder of Integral Recovery® and his book Integral Recovery: A Revolutionary Approach to the Treatment of Alcoholism and Addiction  won the 2013 USA Best Book Award. John also hosts interviews with leading innovators in the spiritual technologies field on Spiritual Technologies 2.0 Live and co-hosts the popular Journey of Integral Recovery podcast.
I have read something different about theta waves and learning languages. A University of Washington study tested students resting brainwave activity before learning French. They found that students with a higher amount beta/gamma and a lower amount of delta/theta activity were better at acquiring a second language. When you are dominant in theta, that is the lowest and most deeply relaxed awakened state you can be in. I think it would be much harder to really concentrate, fully understand and learn new information while in a theta state, so I would personally consider using theta while studying.
Robert Monroe, a radio producer and executive published a popular book called Journeys Out of the Body about his out-of-body experiences when using brainwave entrainment. He later founded an original brainwave entrainment audio company, Hemi Sync. In 1981, the book Mega Brain by Michael Hutchison brought brainwave entrainment information, techniques, and terminology into the popular press.

One can also learn to control and slow down their brain waves through various neurofeedback technologies such as electroencephalograph (EEG), galvanic skin response (GSR), and heart, pulse and breath rate monitors. These devices measure stress and relaxation parameters and then "play" back the signals to the user so they can use the signals as a beacon to guide and "steer" themselves into a relaxed state. This takes some time, work and discipline but is much quicker than learning meditation.
Beta waves are the most common and most prevalent in the brain. These are the brain waves of alertness, dominating your normal waking state of consciousness. The Beta state relates to “fast” activity with neurons firing abundantly, in rapid succession, with attention focused directly towards cognitive tasks and the outside world. Beta activity is engaged in focused mental activity, problem solving, judgment and decision making. New ideas and solutions to problems flash like lightning into your mind.

Maybe a favorite popular song, a certain piece of Classical music, a raucous dance beat, the pulse of Reggae, Indian, or African drums, or the chanting of Gregorian or Tibetan monks, but you probably know how the sound of music, drumming, or chanting is capable of transporting you into an altered and joyous state of mind and uplifting your spirits.

Hi. This article contains a lot of information about brainwave entertainment. Thanks. I have a question. I downloaded an Android app that plays isochronic tones. I like to use an Isochronic tone at 2.5Hz that is in Delta range and is supposed to help me get a deep and dreamless sleep. I use it without headphones and just keep the smartphone next to my pillow. But I do not know if I should keep the tone playing all the time while I sleep or put it on timer to shut off after some specified time. A custom timer is possible with the app. Can you please guide me.
The quickest way to relieve stress is to release endorphins through exercise. An easy way to do this is through shaking and dancing, a form of expressive meditation that loosens your joints as well as clears the mind. It’s one of our favorite techniques to teach in conflict and disaster areas, such as Haiti. Start by standing with your feet shoulder-width apart, knees slightly bent, shoulders relaxed, and shake your whole body for a few minutes (we recommend 7-8 minutes). Then, stop for a minute or two and pay attention to your breathing and physical sensations. Finally, turn on fast music – anything that gets you energized, and allow the music to move you. Don’t feel the need to follow any specific dance moves, just do whatever feels good for you in the moment (it might help to close your eyes). Dance for about 5 minutes, or until you feel satisfied.
Beginning with greater influence on our health, our connection with the universe will lead to enhanced insight and creativity and our ability to influence the evolution of reality, clearing a pathway towards harmony and peace in our lives and in the world-at-large. Using Sacred Acoustics recordings and other methods, we can discover an inner stillness deep enough to connect with our divine spiritual nature. With Living in a Mindful Universe, we show readers how to achieve this same access to the Collective Mind.
“Like the pulses of vibration that produce sound on a guitar string, your brain also creates pulses of vibrations. These vibrations are electrical impulses,” continues Naik. “Their activity can be measured by using an EEG (electroencephalogram), which measures the frequency of these pulses [which is measured in Hertz]. Your brain actually has a predominant frequency at which it operates in any given moment; this can be associated with your state of mind.”
If brainwave entrainment leaves you with unwanted side-effects (see below) or discomfort, you’re probably encouraging a range of brainwaves that are already excessive in some area of your brain. The way around this is to get a brain map to see what your brain’s strengths and weaknesses are, and see what (if any) brainwaves could use some encouragement. 
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