Ross Allan, 29, a chemistry teacher who was on the bus, told how an official from the fire brigade had informed him no-one was missing in the wake of the incident.
Mr Allan was giving evidence at Lanark Sheriff Court into the death of 17-year-old Natasha Paton. Natasha, from Cleghorn village near Lanark, died after the bus collided with a bridge on the A73 near Biggar and tumbled down an embankment.
Raymond Munro, 63, was at the wheel of the coach taking 39 pupils and staff from Lanark Grammar School to Alton Towers in March 2010.
Under questioning, Mr Allan, who suffered a broken wrist, broken hand, a three broken ribs, said he and a colleague, Alison Murray, had tried to complete a headcount.
He said: "Two police officers arrived and they got me and Alison to go and do a headcount. I did one side of the bridge and Alison did the other side. But it was very difficult to know where everyone was because members of the public were helping by taking pupils into their cars.
"At no point did any pupil tell me anyone was missing. After the first count the numbers didn't match to what they should have been. The initial count was 36 and the police told us to do another count. It wasn't until the fire brigade arrived that they took control and got everyone in the one place. The pupils were put into the back of an empty truck. We were then told everyone had been accounted for."
Asked who had told him that, Mr Allan said: "As far as I know he was a fire chief. He wasn't a police officer."
The inquiry later heard from Laura Kyle, 29, a market research executive who was an adult supervisor on the trip. She told of hearing a pupil say her friend was missing following the crash.
She said: "It was quite chaotic, it was still very dark and the pupils were running around looking for each other. I remember a girl saying to someone that she couldn't find her friend. I didn't know any of the pupils' names. I think she did say a name. I just didn't remember it."
The inquiry heard from Scott Mitchell, 30, another supervisor on the trip, who was critical of coach driver Mr Munro.
He said he believed Mr Munro had approached a bend before the accident site with too much speed. He said: "About 50 yards from the crash site I had a feeling we were carrying too much speed to take the corner. The driver applied the brakes and that caused the wheels to lock.
"I could feel we were sliding. He applied the brakes with a significant amount of force. He applied them too late and too hard."
The inquiry will resume on Tuesday.