KEEP IT SIMPLE: What do Edmodo, ClassDojo and Remind 101--all of whom have raised sizable rounds--have in common? 1) They don't have a clear revenue plan; 2) They boast boatloads of users; and 3) "They are all relatively simple technology," writes Re/code's Liz Gannes. Their business models "come straight from the consumer app model--get a bunch of users now, maybe do a 'freemium' model later. They are texting-for-teachers, Facebook-for-classrooms, online stickers and flash cards. They are really quite basic." Now, about those returns on investments...