The 'angry and intimidating' dad apparently spotted the two primary pupils squabbling and raced onto the dance floor, shouting and swearing.
He then dialled 999 and accused one of the primary school children of assaulting the other.
The father's actions immediately brought the disco to an end at the 280-pupil St Andrew's and St Mark's Church of England Junior School in Surbiton, Surrey.
The kids, aged between seven and 11, were then escorted out of the 'disco' after the incident last Thursday.
Police arrived at the school and spoke to the 'upset parent', but no action was taken.
In a letter sent to parents, the parent-teacher association (PTA) wrote: "A parent of one of the children was on site when the incident happened and took it upon themselves to resolve the situation despite the PTA trying to step in.
"This was inappropriate behaviour on behalf of the parent and it came across as angry and intimidating.
"The parent also took it upon themselves to call the police who did attend the school.
"Unfortunately the children in the hall witnessed this behaviour."
One mum, who asked not to be identified, said: "I heard about this from my son who said this guy just flew onto the dance floor and pulled these two children apart.
"He was shouting and screaming about one hitting the other and then he pulled out his phone and called the police and reported one of the children for assault.
A spokesman for Kingston Council said: "We take these matters extremely seriously, and the school has written to all the parents assuring them that the disco was constantly supervised.
"It is such a shame that a lovely event, usually enjoyed by all, was marred by the actions of one parent.
"We understand that this incident will have been very stressful for the children who witnessed it and the school will support them in any way needed."