Math SAT Practice

I teach a SAT Prep course at our high school.  We are on trimesters (12 weeks), and myself (Math teacher), the English teacher, and the Reading teacher swap groups of kids throughout the 12 weeks.  I have each group of kids for about 18 days.  The goal is to look at PSAT 10 scores, take a practice Math SAT at the beginning of the 18 days, practice skills throughout (on Khan Academy), and continue taking practice SAT tests (4 total), and to hopefully see an increase from PSAT 10 Math score to SAT score at the beginning of course to SAT score at the end of course.....

So... a huge part of the course involves the Khan Academy Math skills practice offered.   Each students is required to take all 41 math skills on Khan Academy and improve them.  Khan gives a starting 'skill level' from 1-4, and students must improve each skill ONE skill level over the 18 days.  

Very LONG story short - I've discovered there's a way to cheat :(:(:(:(:(.  If the kids ask for a 'hint' enough times, it'll tell them the correct answer - then the kids can refresh the page, and it's as if they never asked for a hint at all.  So I have a few lovely students who have learned this - and are going through each skill and hitting hint, collecting the correct answer, and then refreshing. 

Any ideas on how to stop this (other than letting the kids know this is super ridiculous as they have pretty low SAT scores right now, and the real SAT is in like a month!!!!!!!!!!!  ... not to mention they all think they're going to MSU and U of M with a 950 on the SAT)