Police said they received reports of a child being approached by a man outside The Oaks Primary school in Loppets Road, Crawley, on Tuesday (December 7) at around 9am.
A police spokesperson said: "The man, who was not known to the child, is reported to have briefly grabbed the boy’s hand before walking away.
"He was unharmed and continued on his journey to school."
Sergeant Karina Puttock, of Crawley and Mid-Sussex's Neighbourhood Policing Team, said: “We understand incidents such as these are concerning for the community, particularly for parents of young children.
“We are investigating the exact circumstances of this report, which we believe to be an isolated incident and officers from the Neighbourhood Policing Team will be carrying out targeted patrols in the area around school pick-up and drop-off times to provide a visible presence.
“If you have any concerns, suspicions or information which may be relevant to the investigation, please speak to officers directly, contact Sussex Police online or by dialling 101, quoting serial 367 of 07/12.”