Parents at an overcrowded primary school where children are taught in the corridor are blaming their county council for the cramped conditions.
Pupil numbers at West Green Primary School in Crawley have shot up from 104 to 172 since its last inspection in 2005.
Two year groups are taught together in a single class of 40 pupils to try to cope with the situation, with some children being taught in an alcove in a corridor.
But school governors say West Sussex County Council is refusing to provide extra space until numbers hit the 180-pupil mark.
They appealed to parents to support a letter-writing campaign to the council and the Government to try to get an extension to the 1950s buildings.
Parent governor Andrew Coleman told The Argus: "It is disappointing we have had to resort to this to try to get the council to listen to us."
The problem started when the school changed from a 'first' school, taking children up to the age of nine, to a primary school, with children staying on until they are 11.
Before that older children would spend two years at another primary school before moving on to secondary education.
The number of applications for admissions rose when the year groups changed.
Mr Coleman said: "I don't think the council realised how successful it was going to be.
"We began to run out of physical space."
The school has only six classrooms for seven year groups.
West Green's last Ofsted report in 2005 said pupils - one in five of whom do not speak English as their first language - progressed well and showed "good" achievement.
Inspectors praised the school's leadership and management.
Headteacher Julie Dowling said: "Although plans have been developed to extend the school, we do not have a definite start date for these improvements and we face another year in inadequate accommodation and with a temporary classroom."
A spokeswoman for West Sussex County Council said the local authority will provide a new classroom in September. She said the council will avoid using huts for temporary classrooms "if at all possible".
She said: "The county council is currently working with the school to provide a seventh classbase and additional facilities to support the school's infrastructure.
"This additional classroom will be an interim arrangement while the design of the permanent solution takes place for a start on site later this year."
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