Barbara Rogers, headteacher of St Patrick's RC High in Eccles says Kyle Darker was a popular pupil who didn't appear to have any problems at school.
Staff and pupils held a special assembly this morning. The head has been to see Kyle's mother this morning to offer her support.
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The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.
Prime Minister Theresa May announced the decision from Downing Street.
In her message Theresa May praised the "inspirational bravery" and "unbreakable spirit" of Mancunians in the wake of the blast.