Brammetje Baas has sympathetic characters, but a flawed and unbalanced story. It suffers from a problem you see more often in movies based on a book (in this case a cartoon by the screen writer herself): three quarters of the movie are basically the first act, after which there is, of course, not much of a second act and an underwhelming finale. The main principle of good storytelling hasn't been followed: the protagonist is actively trying to solve a problem. The main character here, six years old Brammetje, doesn't really do anything to solve his problem (having a grumpy new teacher who doesn't understand him), because he can't. His parents do, a bit, but ultimately it is his substitute teacher (who appears after three quarters) who does understand Brammetje and gets him to apologize to grumpy teacher, which clears the air. So, for most of the movie, we're watching a boy getting in trouble in class again and again, and his parents trying to deal with it. It becomes repetitious after a while. It's hard to stay engaged, this way.

On a side note, for anyone interested in camera's: this movie was shot on an Arri Alexa with no additional lighting most of the time (only a reflection board) and only basic color correction has been applied, but no artistic grade. So if you want to check out what images of the original Alexa look like, this movie is a good opportunity.