I had to work a lot harder than I'd
expected. You will too.
The good part is that you'll learn a ton, and all of it is directly
applicable to working with children and helping them really learn
mathematical thinking.
Start early, and make sure you are not working a lot or taking a lot of
other summer courses at the same time. This is a course that takes
concentrated time, good access to technology, and some computer knowhow
(or willingness to learn) on your part.