The teachers union has said the conviction of a Gwynedd head teacher under health and safety laws will "horrify" his education colleagues.
Kian Williams, aged three, was hurt jumping from a step
James Porter, 66, was found guilty of breaching health and safety laws after a three-year-old pupil fell from steps and died in hospital a month later.
Dr Chris Howard, of the National Association of Head Teachers, said the case will "scare many head teachers".
He said it took "the whole level of responsibility in to another sphere."
Porter was convicted by an 11-to-one majority after a seven-day trial at Mold Crown Court.
The court heard three-year-old Kian Williams died in August, 2004, a month after being hurt jumping down steps at Hillgrove, a private school in Bangor, Gwynedd.
The kindergarten pupil, from Bethesda, had jumped four steps to the bottom of a flight of brick steps and landed face forwards, causing head injuries which led to a coma and pneumonia.
The prosecution said Kian had been allowed unsupervised access to the steps which exposed him and the 10 other three and four-year-olds in the kindergarten class to a risk to their health or safety.
A health and safety expert told the court the boy's fall was like "falling from the arm of a domestic settee".
The jury was told there had been only one teacher on duty supervising 59 pupils when the incident happened during the morning break.
The prosecution said more staff should have been on duty, and there was no reason why a gate erected following the accident in July 2004 could not have been put up before.
James Porter was bailed to be sentenced in September
Kian's parents said they hoped the publicity surrounding the case would prompt other schools to check their supervision and possible hazards.
Porter, who also owns the school, who had denied breaching health and safety laws, was bailed until the 28 September for sentence.
After the case on Tuesday, Porter's solicitor said the verdict on the "one-in-a-million" tragedy could have "profound implications for the teaching profession and teachers".
Speaking on Radio Wales on Wednesday, Dr Howard, who is also head teacher of Lewis School in Pengam, said head teachers would be horrified that Porter had been found criminally negligent.
"I think it will frustrate and scare many head teachers across Wales because when it comes down to it, on a daily basis, whether they occur with children playing in playgrounds or school trips or whatever it is, calls about health and safety features are the head teacher's call."
Dr Howard said schools were "bombarded" with health and safety advice which, though relevant for protecting children, "does over time have the effect of cocooning youngsters and making head teacher and governing bodies err on the side of caution".
He added: "The effect of that is that we will be limiting activities.
"In some parts of the country, for example, school trips have become a thing of the past because teachers, head teacher and governing bodies won't authorise them."