I think some services need more minutes added to the timetables around school times as I often experience services running late around these times.
An example, the 1537 7 from Durham Bus Station has 4 minutes to get from Durham Bus Station to Nevilles Cross but because of all the schools in this area the service always gets butchered some days it can take 10 minutes other days it can take even longer.
Today the service ended up running over 10 minutes late yet it arrived in Durham on-time.
Late running records