Train Rayleigh > Shenfield > Chelmsford.
X30
Regal Busways route 3.
Train is quick, flexible and easy and you can get discounted season tickets
https://www.elevenplusexams.co.uk/forum/11plus/viewtopic.php?f=15&t=48679Loads of pupils for several schools use the train, particularly for the Chelmsford schools. Changing at Shenfield is simple, as there are not many platforms to choose from. It is an easy walk from Chelmsford station to the school and using the train gives the most options for taking part in after school activities, socialising with friends after school etc.
X30 Is quick, easy, but not so flexible and more expensive.
No.3 bus only really a good idea if you live somewhere on its route and can't easily get to the station for the train or the X30. Almost as inflexible as a one-off private coach service.