Our Lady of Sion School, in Gratwicke Road, Worthing, underwent a three-day inspection by the Independent Schools Inspectorate, who rated their academic achievement 'good' and their personal development 'excellent'.
In his report, inspector Richard Mannix described teachers as well-qualified and said they had a "passion" for the subjects they taught.
The students themselves were seen to have good numeracy skills and excellent reading skills, showing maturity and independence as they progressed through the school.
Mr Mannix said: "The good progress made by pupils is maintained throughout the school across all abilities, because teachers understand and are sensitive to their pupils' needs; in addition they have high expectations both for encouraging pupils' engagement and their standards of behaviour.'
Mr Mannix made particular mention of the youngsters' self-knowledge, self-confidence and emotional resillience.
Headmaster Dr Simon Orchard said: "At a time when negative headlines about young people's mental wellbeing are filling the front pages, we are immensely proud to be recognised for the work we are doing in this area.
"Our starting point is that children do not learn well, and will struggle to go on to lead happy and productive lives, unless they feel positive about themselves and their abilities.
"Through an innovative curriculum, and a dedicated staff team, we ensure that all children can explore their talents, try things out and be challenged and supported to be their best in a small, caring environment."
When it came to future improvements, Mr Mannix suggested staff could provide more of a consistent challenge for more able children when it came to the development of their numeracy skills.
Dr Orchard said: "This inspection report really is a testament to the immense amount of care and attention that all staff – not just those in the classroom – put into ensuring every student can have a successful Sion experience.
"We focus on excellent teaching, supported by careful tracking and communication of students' progress and we add to this thoughtful, holistic pastoral care.
"This combination of challenge and support allows each one of our 423 students to be known for the individual he or she is."
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