It is wrong to go on to high school science textbooks. Those thick and heavy bricks are the sure weapons to kill his interests.

Go to amazon.com to find some light science reading materials with typical kitchen table science experiments. Many good recommendations exist in the resources forum here. One of the things come to mind is the electronics sets they sell at Amazon, my children enjoyed those very much.

Try to keep pushing his reading comprehension. Only in such a way will he be able to start his own journey in science.