The two main teaching unions involved in strike action today say more than 200 schools across Sussex have been closed or partially closed.
Members of the NUT and the NASUWT are striking over pensions, pay and working conditions and by 11am this morning, hundreds of teachers had gathered for a rally in Brighton.
Teachers are objecting to proposals by Education Secretary Michael Gove to bring in performance-related pay, increase their workloads and make changes to their pensions.
Phil Clarke, who represents teachers from the NUT in part of East Sussex said: “The support has been massive already with hundreds at the Brighton rally.
“Teachers are striking as a last resort. Those who are ten years off retirement face a retirement age above 65 - it could be 68 years or older - and our working conditions are being taken away with less time for planning.”
Education minister David Laws has described the strike as “bad for pupils and bad for parents” and said government policy would not change.