An Adelaide man convicted of giving his partner's four-year-old son a "wedgie" so severe it constituted an assault, has had his sentence downgraded.

The 25-year-old, who has not been named to protect the identity of the victim, was found guilty of three counts each of assault and indecent assault.

The District Court was told the attacks, over a three-month period, involved hitting the now five-year-old boy on the bottom with a spoon, flicking his genitals and giving him a "wedgie" so severe it left abrasions on his skin.

The court previously heard the man was engaged and preparing to marry the boy's mother, who continued to support him and no longer had access to her son.

At the time of the verdict, Judge Wayne Chivell commended the boy for giving evidence at the trial, though he admitted he was initially sceptical that he could satisfy the legal requirements to testify and be cross examined.

He said the boy knew the difference between the truth and a lie and he was impressed by the boy's candid evidence.

The man was sentenced to three years in prison, but appealed against his convictions.

In October, the Court of Criminal Appeal overturned the conviction relating to the "wedgie", finding there was not enough evidence to prove the boy's injuries were the result of any crime by the man.

Today it was tasked to resentence him for the other five convictions, and ordered he serve two and a half years in prison.

It fixed a revised non-parole period of one year and 10 months - backdated to the date he was taken into custody last July.