School's out but that doesn't mean knowledge gained during the year needs to be lost forever. Summer brain drain is a real phenomenon and a lurking threat for school-age children.

According to the National Center for Summer Learning at Johns Hopkins University's School of Education, most students lose about two months of grade-level equivalency in math computation skills during the summer months. Decades of research also have shown that students typically score lower on standardized tests at the end of summer vacation than on the same tests taken at the beginning of the summer, the center's website states.

But parents can help keep their kids from losing lessons learned by making a few simple changes to summer activities, said Susan Canizares, publisher for Houghton Mifflin Harcourt's K-12 division and an elementary education expert. It's important not to change summertime into school time, she said, but one of the best practices is to take activities that the family is doing anyway and find lessons within them.

"We all play, we all shop, we all eat," she said during a phone interview from her Austin, Texas, office. "It's about how you can take some of those activities and get some educational value out of them."

Some ideas for parents:

Follow a favorite sports team. Help children track scores and favorite players' statistics. Keep a chart with each family member's prediction on scores and game outcomes, and at the end of the season, analyze to show who had the highest percentage of winning predictions.

Plant a garden. Children can research what grows best in the neighborhood, chart growth and experiment with different watering cycles.

Go shopping. Challenge kids to buy food to feed the whole family lunch or dinner for $12 and have them try to decorate the table for less than $2.

Get cooking. Have children find recipes in cookbooks or online, and have them plan a family dinner where they'd have to double or triple the recipe.

Read aloud. It's a myth that some children are too old to be read to, Canizares said. Even children in middle school like hearing a story from a parent. "To listen to someone read to you is a relaxing, enjoyable experience," Canizares said. Hit the library for new-to-you children's books.