I have recently done a few days’ supply teaching. I’m a total novice at supply and it was with massive trepidation that I set out into the unknown, clutching my CRB report and emergency worksheets. As I’m only free for supply one day a week, I was going to be one of those transitory teachers who materialise before a class once and then disappear, never to be seen again. Visions of unfriendly staff, unmanageable children and rioting classes rampaged through my imagination.

It hasn’t been as bad as I expected. The teachers have been friendly, no one’s thrown a chair at my head and I’ve always managed to find the toilet. What has been a bit of an eye-opener is how varied primary schools can be, even within the same square mile. I’ve also become particularly wary of rainbows.

Rainbows crop up a lot in certain schools. They are painted on windows and appear in school logos and entrance halls. They make me nervous because in my (admittedly very limited) experience, the larger the rainbow the more stories of heartbreak and deprivation you are going to find at the end of it.

At the school with the biggest rainbows, I spent the day with Year 1. On my way to the classroom, I passed rooms called things like “The Place 2 Be” and “The Chill Out Zone”. You only get these rooms in certain postcodes and they normally contain beanbags, a lava lamp and a tired but smiling woman wearing a bright cardigan and an identity badge round her neck.

The class teacher pushed some planning into my hand and smiled. “Watch out for Riley,” she said. “He might not do any work - it depends on his mood.”

It was a freezing cold day, with snow on the ground, and one child arrived without a jumper. Another had thin socks and plastic “jelly” shoes on her feet. Their teacher had them well trained: they sat quietly on the carpet with books, responding well when I took the register and asked them to tell me about themselves.

Riley turned up late, his mum literally shoving him through the classroom door. He threw his bag on the floor and glowered around him. The teaching assistant (who was wonderful) coaxed him on to the carpet.

The morning whizzed by in a blur. The children clearly struggled with maths and English but were keen to learn, sat attentively while I read stories and were desperate to tell me things; some of them, in that way that is particular to five-year-olds, half climbed on to my lap to try to get my attention.

Teaching in a school with large rainbows, you learn new tricks fast. “Use the antiseptic gel whenever they touch you,” the teaching assistant recommended. “There’s a lot of ringworm going around.” She also told me not to even attempt to get the children writing until they’d had their milk and fruit. “Most of them won’t have had any breakfast,” she explained. “There’s no point trying to get them to concentrate on an empty stomach.”

Riley spent the morning alternately kneeing his classmates in the back as they sat on the carpet and lying under the table wailing when we tried to make him sit up and do some written work. I eventually got him to take part by letting him hold a furry tiger I had brought in. “Don’t worry about him,” the teaching assistant told me. “He’s actually having quite a good day.”

In the afternoon I managed to penetrate Riley’s defences a bit. The children did painting and drawing activities and we let them build Lego castles as part of their topic. Riley built his with incredible concentration and even deigned to read to me. His mood changed when I picked another child to wash the paint pots and he retaliated by smashing his castle.

While I marked their work after school, the teaching assistant filled me in on Riley’s home life. His dad was mostly in prison; his mum had a serious drug habit and anger-management issues. “She can be high as a kite and friendly as anything, or will just grab him without making eye contact,” she told me. “Riley’s at his very worst when she’s affectionate, though. He’s so used to screaming and shouting that he just can’t cope when his mum’s calm.”

“What do you think will happen to Riley?” I asked her. “He’ll go the same way as his dad,” she said. “I’ve seen it happen too many times. He’s got too much anger and he’s only 5.”

I had a sinking feeling that she was right. The school was doing its best but it only had Riley seven hours a day, 39 weeks of the year. The rest of the time he was with his family. I couldn’t see how a rainbow, however large, could counteract that.

Jo Brighouse teaches at a primary school in the Midlands.