Is the joint rabetted or a full 3/4? If full 3/4, try 1 5/8 drywall screws. 1 1/4 screws only have 1/2" of purchase going through the 3/4" material. If it's rabetted to 1/2", they maybe okay, but 1 5/8 would do no harm.
Casey

You should get some real screws designed for wood.
Bugle head screws tend to cause splitting, especially near the edge of plywood.

McFeeley's has a good selection of screws.

Here is a link that might be useful: McFeeley's

I'm in the anti-drywall screw camp also. They are not designed for wood joinery. It sends a chill down my spine when I see and remove them from new factory-built furniture. Rockler also has decent screws if you don't want to mail order and you have a store nearby. I am not familiar with "Norm's plan" but if it's using pocket screws, those work best with a screw designed for the application.

The other problem may be your plywood. I have seen some real junk from China via the home centers. The inner plies are mush and held together with something just slightly more adhesive than spit. All I'm buying now is 100% poplar core domestic.

Pet peeve: I never "pre-drill" a hole. I always just drill a hole because I'm not smart enough to figure out what "pre-drilling" means.

Here is a link that might be useful: about drywall screws

Again, thanks for your input and help. Its always good to know the opinion of the professionals.

Haefele - Zip-R Screws, no pre-drilling required. Type 17 Auger.

I'm in the middle of a library/office build, and the cabinet carcasses are all 3/4 birch ply, the shelves doubled up 3/4" ply.

As to the box construction, where a fixed shelf or partition meets a sidewall I plow a 1/4" by 3/4" dado into the sidewall to capture the shelf.

Where carcass tops and bottoms meet the sidewalls, I plow a 1/4" by 3/4" rabbet in the top/bottom edges of the sidewalls.

I use 1/2" ply for the backs and plow a 1/2" by 1/2" rabbet in the back edges of the sides/top/bottom to capture the back panel and square the box.

Screws? I never use drywall screws. I glue (titebond) and screw 3/4" birch to 3/4" birch with 1-5/8" screws. And use 1-1/4" screws when screwing the 1/2" ply back to the 3/4" ply sides.

If using veneered MDF core sheets, I'll use confirmat screws. Brickeye gave you the link to McFeeleys, they are a great resource.

Pre-drilling? For paint-grade cebinetry all I use is a properly sized and tapered countersink bit. I then putty the screw holes.

As to the screws stripping out, if he's using fine threaded drywall screws that could be part of the problem. Fine threads are for metal studs. And while many people still use coarse threaded drywall screws for woodwork, drywall screws are for...drywall.

Or his drill bit could be too large, it should not be larger in diameter than the diameter of the uncut screw shank. Slightly smaller is better for softwoods like birch ply.

Or he needs a gentler touch with his drill trigger finger.

Even if he goes to a box store and buys a box of coated deck screws, those would be better than drywall screws. Better threading, better shear and tension strength.

Mongo

Hi, I just checked back in. Thanks Mongoct for your great information. Know that this will continue to be a great resource for others who follow. He is almost finished assembling the boxes and did use the construction method you suggested. He also has been countersinking, I'll have him read the post for the screw advice too. Thanks again guys.