The first day of school gets as many as four and a half stars in his diary. This is because Bert falls in love with the coolest ninth-grader also known as "Yogurt Leila". Luckily, Leila’s sister Amira is in his class. To get closer to the older sister, he makes friends with the younger one. When Bert finds a diary on Leila's bed, he’s tempted to read it. How better to impress a girl and pave the way to her heart, if not by knowing her secrets? But is that really fair? Bert certainly makes a mess of things...
The film is based on a series of novels written in the form of a diary, by Swedish writers Anders Jacobsson and Sören Olsson, best known for their books about Sune.
»I acted as a 10-year-old myself, in a big Swedish production that was very popular on television. I had quite extensive experience as a child actor, but it wasn’t always enjoyable. That's why I was determined not to go there again. Bert's story is nice, we don't plumb the dark depths, so we didn’t have to face that.«
– Michael Lindgren