Schools in Hatfield and Brookmans Park have relaunched as members of the same academy trust at the start of the new term.
Onslow St Audrey's School, which has been an academy since 2012, joined Danes Educational Trust this week, while Chancellor's School made the decision to work with the trust in July.
David Bullock, headteacher at Onslow St Audrey's said: "We have already been working closely with staff from the trust over the past 18 months, the benefit of which was reflected in sections of our most recent Ofsted inspection and has been evident in the progress of our fantastic students this year."
Onslow St Audrey's School was given the overall rating of 'requires improvement' by educational inspector Ofsted in June with 'good' in three categories and 'requires improvement' in two.
The report acknowledged that Mr Bullock had "established a culture of raising aspirations at all levels" and recognised that "the new head teacher is making a positive difference to the school" and has "quickly won the trust of the wider community".
Reacting to the overall rating, Mr Bullock said he is not going to focus "on chasing Ofsted ratings", but on making Onslow St Audrey's "the best school it can be".
"Feedback has been overwhelmingly positive and students feel safe and happy to come to school," he said.
Mr Bullock added he was "delighted" that the school has become an academy and was looking forward to "an exciting future as part of the trust".
The Danes Educational Trust was formed when St Clement Danes School, an 'outstanding' school in Chorleywood, was asked to open a second school in South West Hertfordshire - Croxley Danes School.
Its chief executive, Dr Josephine Valentine, was headteacher at St Clement Danes for 20 years and is thrilled to be welcoming Onslow St Audrey's School into the multi-academy trust.
She said: "I am excited to continue to work alongside these four exceptional headteachers and their staff to share their existing good practice across our schools and deliver sustained improvement for students as a result of this collaboration."
Both Welwyn Hatfield schools will keep their own ethos, name and uniform but students and staff will be able to work with the trust on recruitment, training and projects of an educational and resourcing nature.
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