Adult + School child should catch the normal bus (non school service)

Does anyone know which type of bus we need if an adult is travelling with a school child? Is it a school bus or a normal one? Thanks

Thank you Goldhawk - we are getting there! We need to get an earlier one as the exact one we need is a non school one! Typical! 

Unfortunately the real time information doesn't show which buses are school service and which aren't
However the next 319 should have been a school service

The 319 is every 7-10 mins in peak times so your child will need to allow more time

Does anyone know how this actually works? My daughter had her first day at school today and we went to get the bus but when the 319 turned up, he wouldn't let us on as it was a non school priority bus. So we had to go home and get the car so we weren't late -
My daughter is starting at secondary school and will need to take the bus to and from so relying on the car won't work plus I have another school run to do for my youngest - 
I understand there are some priority buses but how do you know which ones are and which ones aren't so you aren't just standing at the bus stop for ages? 
Thanks!