while solving a lathoa case, if you spot the error you get back an amount of points. if you score also the explanation exhibiting your understanding you gain more points.
But what are the points used for?
Getting kids addicted to something useful.
XP moves a kid up the detective ranks, from Rookie to Sherlock. At 2000XP a leaderboard unlocks, but only if a parent turns it on. Nothing to buy there..