This is my suggestion, too. When my son was in high school, this was the beginning sewing project in one of his living classes. Most kids like the lounge pants and these are good in flannels or lightweight fleece.

I'd gonwith the pillowcase idea. Or a laundry bag...French seams for that would make it sturdy and is something a boy of any age could use. Have fun!

I used the book Buckles and Bobbins, I think it's called. My ten year old son won a blue ribbon at the county fair for his duffle bag. He even made one for his best friend. He's sixteen now and they both still use them.

A private school here in town pays me to teach 5th thru 8th grade kids during their summer camp. I give the parents a list of four online quilt shops and the parents let the kids pick out three charm packs. We have donated sewing machines and the kids make a lap quilt for themselves, using a flannel sheet for backing. They do great at sewing the patches together and then quilting in the ditch. In all the years I've been doing this only one child could not manage to sew. The other kids pitched in and made her quilt for her!

I think I would take him to the nearest fabric store, sit him down with the pattern books, and let him chose something to make. That way, no wrong choice of project. Suggestions might be PJ bottoms, pillow, pillow case, costume for Halloween, a gift for his mom or girlfriend, etc. This also gives you an opportunity to talk about appropriare fabrics for the pattern, notions, thread, etc.

It's amazing what people can do it it's their idea to do it.

Last summer I taught my 19 y o grandson how to sew a pair of shorts (jams). Very simple-no pockets, elastic waistband. He's still wearing them.
this year he made a robe for his girlfriend from silk he had purchased in Thailand. Again a very simple pattern.( she loved it!)

A messenger bag big enough for a tablet or laptop. First make a sleeve with something thicker (I use 2 flannels with a strip of batting at the bottom) to put the tablet in and then it is a removable insert for the bag. Make the bag in a darker brown or blue denim and make the lining something he does (sports, comic book heroes,cars, etc.). The bag is mostly straight sewing lines but has several good techniques to learn (straps, lining,pockets). This is one of the projects I would teach during my summer classes of girls and boys ages 10 - 17. There are many free patterns for messenger bags available online.

I've been teaching my grandson about sewing for the last couple of years. When they were first beginning I gave them "lined binder paper" I removed the thread from the machine and just let them practice sewing on the lines. They were good about staying on the lines and they also developed confidence about sewing. We then moved on to pillow cases. They love to make PJ bottom for themselves. The younger grandson uses my featherweight because he says it's "Just his size". He is now 8 and has been sewing for 3 years. Anytime they see me sewing they want to sew with me and I welcome them.

Do the railroad quilt. It is quick and easy and you can even turn it into a placemate. I started my husband off on it and it gave him practice with getting his seams correct. I told him think of the sewing machine like a router only instead of wood you are cutting fabric and you have to be careful of the needle. Everything has to adjusted correctly before it works. Hope this helps. Good luck.