Education block - allow some classes to come later or to leave school earlier.

manually set educational block,

The program calculates the amount of lessons per each day automatically.

If you for example have 32 lessons per 5days in a week then the software calculates 32/5 = 6.4. So the automatic lessons distribution decides that this class has to have 6-8 lessons each day. In this case the software can spread the lessons like 6+6+7+7+6, or 6+8+6+6+6. It will not generate 9+5+5+9+4

Also the software starts with 1st lesson and fills the education for each class until the calculated max per day.

This automatic teaching block calculation is good for most of the schools. However if the class has 32 lessons and you want to allow 5-9 lessons each day, you have to set the teaching block manually.

In Class -> Constrains -> Advanced you can specify that the children can go home after 5th period, but not later than after 9th period:

Exactly the same way can be used to specify that some children can come later to the school. This comes especially handy if you have rooms or teachers shortage. If some children can start one or two lessons later than the others, then it might help to spread the lessons and solve the room/teacher shortage.

On the following picture we have specified that children from 5.A can come to the school at latest on the 3rd lesson (they cannot come later, but they can come anytime sooner):

Please note that this not necessarily apply to the whole class. A part of the class can come later and stay longer, while the other part will come sooner and leave later on the other day. This is especially handy if both groups are using the same room or the same teachers teaches both parts of the school.

The education block sets when the children can start and end their education. This basically sets min and max lessons per day they can have. You can specify it even furher if necessary. See Can I set the min/maximum number of lessons per day for one class?

A bit more on educational block can be found in this article:
Education block - Checking of gaps in class timetables