The St Patrick's pupils were inspired to help by the stories of one of their classmates, who was a foster child, Paddy's Army member Izzy Gibson said.
"We thought that we're so lucky to have all the things that we have, when some people are being taken out of their homes in the middle of the night to go to a family that they don't even know," she said.
They created posters, spoke in assembly to inspire their fellow pupils to help, and did "a lot of nagging" to collect the pyjamas, fellow army member Kate Wield said.
In the past, the pupils have organised a blanket collection for St Vincent de Paul, and they plan to do more to help local charities in the future.
Mrs Worsley said the pupils' effort would make a huge difference to Foster Hope, which works to put together about 5000 packs each year.
"It just blows my mind and I think it's incredible, because 150 pairs of pyjamas means that we can more than do what we need to do this year," she said.
She said the charity still needed donations of things like toiletries, small toys or craft activities.
• More information can be found at fosterhope.org.nz/christchurch.