Okay so if automobile primer, chalkboard spray paint, industrial adhesive, and a couple hours of coat after coat of paint seem like a little too much effort for a kids lap desk a) you're probably right and b) I have a cheaper and way easier alternative to my magnetic chalkboard lap desk for you!
The only thing that will make my 1 year old actually keep a lap desk on her lap for any amount of time is seeing her sister with one. While I was picking up the cookie sheet at the Dollar Tree I saw these little plastic trays and matching placemats. I made this version of the lap desk in less than an hour and $5.50 in materials. Here how you do it.
All you need is a little tray, a placemat, a large and small bag of beans, hot glue, foam core, and super glue.
Follow the instructions for making the pillow (you can find them in my last post, here) and super glue it to the under side of the tray. That's it!