All three played in an under 19 against Kilmarnock last Friday. From a report of the game, Higgins seemed to impress whilst the other two were average and no better than what we have.
It seems Saints boss Gus MacPherson agrees. Higgins has been asked to take part in some more training sessions, whilst former Dundee youngster Cameron and former Manchester City and Celtic player Slack have been told they won't be getting a contract.
Story source: The Official St. Mirren Website