Police are hunting firebugs who set light to a children's play area.
A wooden play hut and a bin were destroyed in the blaze at Barsail Primary School, in Erskine's Park Moor.
The blaze took hold in the grounds of the school at around 9pm on Friday night, and two fire engines rushed to the scene to tackle the incident.
Kat Devitt, a resident who lives nearby, saw the fire at its height.
She said: "One of my neighbours alerted me and I went along before the fire brigade had arrived, and the play hut was on fire and one of the bins was on fire also.
"Myself and another resident had a look to see if we needed to move anything, but we knew the fire brigade were on their way by that point.
"The play hut was totally engulfed.
"I think that is in the Primary 1 to 3 playground."
She added: "There were lots of embers flowing. The play house is next to the bins but the bins are encased in a wall, and the embers had actually gone over into the bins.
"The bins hadn't been set on fire, the embers had set the bins on fire, and the embers were blowing across the school rather than away from the school.
"It's quite upsetting to see.
"That was my primary school when I was a wee girl.
"I work in nurseries and I know how much effort goes into creating a good outside play space.
"I'm very passionate about outdoor play.
"I hate when it's mindless vandalism."
Scottish Fire & Rescue said the blaze was brought under control by 9.30pm.
Police Scotland confirmed it was treating the fire as wilful, and that no-one was injured.
The force appealed for any witnesses to get in touch by calling 101, quoting reference 4301 of 5th April.
