Drop-in sessions at a youth centre based at a secondary school and sixth form attended by more than 1,000 pupils have been cut.
A spokesman for West Sussex County Council said the lunch-time and after-school sessions at Thomas Bennett Youth Wing were cut because of staff shortages.
The youth club is based at Thomas Bennett Community College in Ashdown Drive.
The spokesman said: “We have stopped the regular drop in sessions at lunchtimes and after school for the moment due to staff capacity and are in the process of reviewing the impact of this.
“However, we would stress that whenever staff are in the building the centre is open and young people can drop in to discuss issues and concerns and be given appropriate information, advice and guidance as requested.”
The youth centre’s services were reduced to weekly referral-only sessions.
The spokesman said the county council’s youth support services focussed on young people whose lives were in or could easily descend into crisis following a public consultation in 2011.
The spokesman said: “This means the services now offered are of a targeted and specialist provision for those young people who are identified as being in need. This has meant that some provision which was open to all young people irrespective of need has been reduced.”
Ryan Folan, 13, who attends Thomas Bennett Community College and went to the club, said: “I helped out a lot there.
“This month they cut activities.
“They stopped after-school and lunch-time clubs - pretty much all the clubs.”
A council website stated the centre offered cooking, arts and crafts, table tennis, and learning opportunities for 13 to 19-year-olds and ran activities on school holidays.