The teacher asked the misbehaving child to sit next her and said: "I should take you around the back and give you a whack."
The tribunal also heard evidence the teacher had put her foot under a seated boy's bottom and flicked him off the carpet onto concrete - a drop of about 5cm - after the child ignored instructions to get out of the way of an entrance area.
The teacher, who was provisionally registered at the time, was dismissed from the centre following an disciplinary investigation.
Her lawyer, Stan Austin, submitted the evidence before the tribunal was unreliable and the allegations should be dismissed.
The teacher did not give evidence, which the tribunal said was both unprecedented and inconsistent with her professional obligations to co-operate with disciplinary proceedings.
The tribunal said it had been left to wonder whether the teacher had chosen not to give evidence to avoid an admission.
However, it found there was enough evidence without her co-operation to prove the charges relating to the smacking and the threat.
But there was insufficient evidence to prove she had flicked a boy onto concrete, or that she had left the centre with an insufficient staff-to-child ratio.
The tribunal noted the teacher was inexperienced but, because she did not give evidence, it could not tell whether the behaviour was out of character.
"Any corporal punishment, or threat of violence directed to students by a teacher, is serious. But on a scale of seriousness, our sense is that this respondent's behaviour, as established in this case, is at the lower end of that scale."
The tribunal said it had reached the view, by a fine margin, that the teacher should not be de-registered or suspended.
However, it formally censured the teacher, ordered her to enrol in and complete an anger management course, and ordered her to undertake further professional training.
It also ordered its decision be noted on the teachers' register, required the teacher to advise any current or future employers about the decision for a period of three years, and ordered her to pay costs of almost $5000.