Summer break is a time for kids to hang up the backpacks and relax. But teachers warn that students who don't challenge their minds even a little will fall victim to the "summer slide."

This slip in academics takes place when kids don't keep up their studies during the summer break and eventually fall behind.

Research show students can lose up to 25 percent of their reading skills during these months, meaning teachers spend much of the next year playing catch-up.

"Young people who aren't engaged in learning activities during the summer months experience a huge challenge when they get back to school in the fall," said Ron Fairchild of the National Summer Learning Association. "Teachers often have to spend time re-teaching the same materials they spent teaching the previous year -- sometimes as much as up to four to six weeks."

Kids from low income families who can't afford summer camps and vacations are hit even harder. It takes these students more than two months after the break to re-learn lost skills.

"What we find is that children growing up in disadvantaged families keep up with children from better off families tolerably well during the school year," explained Karl Alexander of Johns Hopkins University. "Where they fall behind is over the summer months. And we've seen this over the entirety of the elementary school years."

It's up to parents to ensure kids don't backslide during summer vacation. Experts say simple stimulating activities can have a huge impact and even put kids ahead.

Most importantly, parents should encourage kids to read over the break. Audio books are also good during long drives.

Take family trips to museums and zoos, many of which can be very inexpensive or free.

Having the kids help out in the kitchen will exercise their math skills. Let them follow the recipes and do the measuring.

It's important for kids to relax and enjoy the summer, but including fun leaning activities will keep their minds sharp and ready for the next year.