Why couldn't he just take Arare-chan and Gatchan* to the amusement park after going to the movies with Yamabuki-sensei? He could tell Yamabuki-sensei that he is going to take the kids to the amusement park after their movie date and invite her to come with them, thereby scoring a double date with the teacher…

*that's short for Gajīra-chan, actually kkkkk