Imma just use someone elses comment cus I also didn't get to that route yet, but basically "...You have to get Rune's jacket and follow Klaus into the woods. After that, go down Devon's route until you get to offer to help him put away the telescopes. Choose to go to the cafeteria instead and you'll be on Klaus's route." - Susie!!^^^.
Hope that helps, also I send my thanks to Susie as well.