A teenager convicted of hate crime for cutting the hair of a Sikh schoolmate in the US has escaped jail time, shocking the community which is already seething after another student was attacked this week.

Acting Queens Supreme Court Justice Joel Blumenfeld ordered Umair Ahmed, 19, to complete 180 hours of community service and write an essay about what he had learned since his attack on 16-year-old Harpal Vacher.

Based on Ahmed's conduct in the next year, Blumenfeld will decide next June whether to put him behind bars.

"What you did was incredibly stupid," Blumenfeld was quoted as saying by New York Daily News. 'Incarceration just can't be the only answer. For this next year, the threat of jail hangs over your head.'

Ahmed faced up to four years behind bars for the May 24, 2007, attack on Harpal, in which he dragged the Newtown High School freshman into a school bathroom, ripped off his turban and cut off his waist-length hair, prosecutors said.

Ahmed was irate over a taunt about his mother, authorities said.

A Queens jury convicted Ahmed of felony menacing and coercion charges, both hate crimes, along with weapons possession and harassment.

The verdict which angered Sikh advocacy groups came as New York City Schools Chancellor Joel Klein personally apologised to another Sikh student who was punched in the face with a set of keys by a teen trying to rip off his turban.

Following a rally calling for more protection for Sikh students, Klein met privately with Jagmohan Singh Premi, 18, who was assaulted Tuesday at Richmond Hill High School in Queens.

Premi suffered an orbital fracture and bruising during the incident, which led to the arrest of his 15-year-old attacker who has been charged with felony assault and harassment.

The classmate had reportedly pulled Premi's beard and called him 'dirty' and a 'terrorist' for months in their English as a second language class.

'I let him know that he can reach me directly if he needed to speak to me,' Klein was quoted as saying by New York Daily News.

'I am afraid to go to school,' witnesses said Premi told Klein at Education Department headquarters where the rally was held. Klein said his agency will distribute anti-bias brochures and is working to expand the system for tracking bias incidents.

Activists were not satisfied with Klein's response, noting that education officials made promises after Vacher's hair were cut off and were unhappy with the sentence awarded in the case.

'The whole thing was a disgrace. It just wasn't an appropriate sentence,' said Prabhjot Narula of United Sikhs.

'For a hate crime, it was a slap on the wrist.'

Ahmed, a Pakistani Muslim who came to this country six years ago, will spend the next year serving at the Elmhurst-based South Asian Youth Action organisation, as well as undergoing tolerance counselling at a Holocaust centre, the daily said.

He'll also have to spend 100 hours at a programme selected by prosecutors.

'We are very pleased with the sentence and think this is a fair resolution,' said Ahmed's lawyer Bruce Maffeo.

United Sikh called the verdict 'grossly inadequate' and vowed to monitor the tolerance training to make sure it includes education about Sikhs.