No one was injured but the Tower Hamlets school, where 63 pupils in two reception classes have English as additional language, has since spent pound;10,000 on extra fences and closed-circuit TV cameras.
Gehane Gordelier, the head of Harry Gosling primary claimed the attack by teenagers was racially motivated. The east London primary, which is in a notorious red light district, last year won the title of most improved school in Britain. It is an oasis inside but outside is not so welcoming, the head admits.
Pupils - who come from families in severe hardship, living in overcrowded conditions with around half sharing beds with siblings - found needles in the playground.
Ms Gordelier warned that attempts by ministers to cut cash to London in plans to radically reform council funding would worsen problems.
Her comments came as the Association of London Government also said academic standards among deprivedcommunities would be hit if the ethnicity factor was removed from the funding formula.
When Ms Gordelier took up her first headship post at the school in September 1998, the 418-pupil primary had a pound;100,000 budget deficit, five classes without teachers and was in special measures.
"We won a record by turning it around in 10 months and ensuring teachers felt valued and supported with clear leadership. If funding decreased, we could not guarantee to sustain improvement."
The school employs 10 English as an additional language teachers with the ethnic minorities achievement grant, and spends an extra pound;60,000 a year on additional support to the children in reception classes.
It has 24 teachers and also employs a literacy team to concentrate on phonics. Teaching assistant Shaliar Khatun is one of them.
"I came from Bangladesh and had problems with English when I came here aged eight. I have seen a tremendous improvement since more funding has been available - it is good to give people a better education."