Brent has a dozen full or overcrowded primary and secondary schools, new figures show.
The Education Policy Institute said areas with schools operating close to or over capacity see teaching staff facing additional demand.
A school is at or in excess of capacity when the number of pupils enrolled is greater than or equal to its number of places.
Department for Education figures show 12 schools were at or over capacity in Brent in the 2021-22 academic year.
Of them, nine were primary schools and three were secondary schools.
Across England, 17% of primary schools were full or over capacity while 23% of secondary schools, including sixth forms, were at or above capacity last year.
The Department for Education said most state schools that exceeded their capacity were over by fewer than 10 pupils. About 7% of schools exceeded their capacity by 10 or more students.
Jon Andrews, Education Policy Institute head of analysis, said the proportion of schools operating at over capacity is likely to fall in the coming years.
"Pupil numbers are already declining in primary, and will soon peak in secondary and special schools. The Department for Education estimate that the total pupil population will fall by over 900,000 between 2022 and 2032," Mr Andrews added.He warned the result of schools operating close to or over capacity is additional demands on teaching staff and pupils being left without their preferred choice of school.
He said: "With our research having revealed that pupils from more affluent backgrounds more frequently succeed via these routes of appeal, it’s likely that disadvantaged pupils will suffer to a greater extent from the effects of schools being over capacity.”
The figures show the most crowded primary school in Brent last year was St Joseph's RC Infant School. The school had 209 students on roll and 180 places – meaning it was over capacity by 16%.
The most crowded secondary school in the area was Wembley High Technology College which had 1,405 pupils and 1,334 places last year. It was over capacity by 5%.
Geoff Barton, Association of School and College Leaders general secretary, said arrangements are put in place to accommodate pupils where a school is over-subscribed.
Mr Barton added: "The bigger issue is that this situation is often driven by Ofsted judgements rather than a shortage of school places in the system as a whole because many parents apply for schools with ‘good’ and ‘outstanding’ ratings.
"It drives up property prices in certain areas and stigmatises schools in other areas."
He said the system "desperately" needs to be reviewed and added struggling schools need more support.”
A Department for Education spokesperson said it has created almost 1.2 million school places since 2010 and added many more are "in the pipeline".
They said: “The vast majority of schools listed as overcapacity are either at or just over recorded capacity, and we work closely with local authorities to make sure they offer a school place to every child in country.”