Do you think its safe to use clear wall tacks in a pre school class? Isn't Scotch Tape safer on walls not made for tacks?

I would never use tacks or any type of sharp object in a preschool classroom. There are so many other ways to mount things that make more sense. For instance, many white boards are magnetic and you can use large magnets (avoid small ones which could be swallowed) and 3M makes dozens of mounting products that are clear, don't ruin wall surfaces, and are non toxic should a child decide they want to put one in their mouth. As a general rule if you can take an object, poke yourself with it, and bleed, it shouldn't be in a preschool classroom.

By the way, Scotch tape is not a good choice for sticking things to walls. In many cases, it's not strong enough to adhere to the wall, and if it's a painted wall, it will take the paint off the wall.