Roedd Ashley Talbot yn 15 oed pan fu farw.
Ar ôl y digwyddiad yn Rhagfyr 2014 cafodd gyrrwr y bws, athro yn yr ysgol, ei gwestiynu gan yr heddlu ac yna ei ryddhau.
Cafodd bachgen arall ei anafu yn y digwyddiad.
Dywedodd Ann Rees, oedd yn cael ei hadnabod fel Ann Carhart yn broffesiynol ac oedd yn bennaeth ar ysgol ar y pryd, wrth y rheithgor fod y ffordd i'r ysgol yn cael ei defnyddio gan fysiau, ceir a phlant ar droed.
Clywodd y rheithgor fod na "anrhefn enfawr" ar ddiwedd y diwrnod ysgol.
Dywedodd Mrs Rees fod staff yn cael eu rhoi ar rota ac yn gwarchod gwahanol ardaloedd yn unol â gofynion asesiad risg.
Roeddynt yn cael eu hanfon i wahanol lefydd hefyd yn ôl yr angen.
Mae'r cwest yn parhau.

Prosecutors said Darren Byrne, 40, struck Maria Byrne, 35, on the head at their home in Theydon Bois after she discovered he was having an affair.
The jury was told Mr Byrne doused his unconscious wife in white spirit and turned on the hob before going out.
At Chelmsford Crown Court, Mr Byrne denies murder and arson in February.
Prosecutor Andrew Jackson said former city trader Mr Byrne and his wife had a row on the morning of 13 February after she found he was continuing an affair with a married woman.
Mr Jackson said: "It's the prosecution case that the catalyst for this alleged murder was Maria Byrne's discovery for the second time of his alleged infidelity."
The court was told that after dousing his wife's body with the flammable liquid he went on a walk with the family dog.  CCTV footage showed he was away for more than an hour.
Returning to find his plan had not worked, he concocted a charade, said the prosecutor.
He called the emergency services to say his wife was "burned" and told the operator: "The stove was on and the frying pan's on the other side of the room. She's not breathing."
Mr Byrne told paramedics his wife had been making him a bacon sandwich and when he returned home she was dead, the court heard.
A post-mortem examination identified white spirit on Mrs Byrne's clothing and a half-empty bottle of white spirit was found in the garage, the jury heard.
The couple had two children together who were not at home at the time of their mother's death.
The trial continues.

The collision, which involved a silver Porsche and a grey Toyota Hilux, happened on the B976 Birse to Finzean road at 19:12 on Saturday.
The 30-year-old driver of the Porsche was airlifted to Aberdeen Royal Infirmary.
The driver of the pick-up was uninjured.
Sergeant Rob Warnock, from the Aberdeenshire and Moray Road Policing Unit, said: "Inquiries into the circumstances of the incident are at an early stage and I am appealing to anyone who witnessed the incident or saw the silver Porsche or the Toyota Hilux prior to the incident to contact the police.''
Clywodd cwest fod yna "anhrefn enfawr" yn gyson y tu allan i ysgol uwchradd ym Maesteg lle bu farw bachgen ar ôl cael ei daro gan fws mini.
[NEXT_CONCEPT]
A man killed his wife and then took their dog out for a walk while he hoped their house would burn down with her inside, a court has heard.
[NEXT_CONCEPT]
A man is being treated for life threatening injuries after his car was involved in a crash with a pick-up truck in Aberdeenshire.