Something’s going on with Sam. Instead of his usual sunny and sociable self, he’s been acting out of character for the past few weeks. Alternately disruptive and withdrawn, it’s as if he’s preoccupied with something. That something is as big a thing as can happen in the life of a young boy: his Mum’s boy- friend, Michael, has moved in.

As Michael’s teacher, you were lucky to hear this news on the school grapevine. If a colleague who is a friend of Sam’s family hadn’t mentioned it to you, you might never have known about this major event in Sam’s world.

For the boy it’s a time of excitement, hope, change and fears. At home, everybody’s being nice to each other. Too nice. Things aren’t the way they usually are. It’s like everyone’s treading on glass. His mother is bending over backwards to ease the transition for the two of them. Michael is taking Sam out for treats and bringing home expensive magazines for him. There are no arguments, no conflicts.

And for Sam, no honesty. It’s all too calm on the surface and too tumultuous just below it. He’s afraid to let on to his mum that it feels so strange. He wants to be nice like they’re being, but his mind is full of worries. Will it always be so calm? Will his mother be able to carry on loving him and giving him the attention he always had before? And will Michael really stay, or will he leave them just as his dad did a few years before?

At times of transition like this, the stability that school represents is particularly important to the thousands of children who, like Sam, find themselves in step-families. Because school is the safe place that it is, in an otherwise radically shifted world, it is there where Sam can act out his fears and anxieties. He’s afraid that if he lets down his guard at home, he’ll drive Michael out and make his mother miserable.

While that helps to explain Sam’s behaviour, what do you do about it? As Sam’s mother hasn’t told you about the new situation directly, tread carefully. Ask him if there’s something going on at home that’s troubling him and offer him the chance to talk to you privately.

If there’s a counsellor at your school, you can arrange for them to meet. If there isn’t, you don’t need special training to be able to let him know that you’re on his side, that you understand how difficult these new changes are for him. But at the same time, let him know that his behaviour isn’t acceptable.

Knowing that he has someone who he can offload to can make all the difference to Sam, helping him get through a transition that may be long and hard but, hopefully, is the beginning of a rewarding relationship.

The National Stepfamily Association runs a helpline at 0990 168388 offering advice, information and support to families and professionals