Oakleigh House in Swansea, the junior school of Ffynone House, is only the third of 62 independent schools in Wales to be assessed under arrangements introduced by the Education Act 2002.
Oakleigh, a pound;6,600-a-year day school with 149 pupils aged three to nine, provides a "broad and rich curriculum and a wide range of extra-curricular activities", according to Estyn.
The agency found pupils to be enthusiastic learners who enjoy their work and achieve high standards. "Within a family atmosphere, staff succeed in promoting the values of honesty, fairness, mutual respect and tolerance," said the inspectors.
In both key stages, pupils' standards and progress in speaking, reading, writing and numeracy are good, said Estyn, while listening skills are very good. Nearly all subjects received grade 2, indicating good features with no important shortcomings.
Science at KS2 gained grade 1, and inspectors noted pupils' "extensive knowledge and understanding of the natural world".
Attendance rates average around 96 per cent for the past 12 months, and the quality of teaching is high, with the proportion of lessons judged to be at least grade 2 close to the average for maintained schools in Wales for 2003-04. Most pupils make good progress.
But the most able pupils do not always work at full capacity and some learning objectives "do not focus on the knowledge, understanding and skills that pupils are expected to gain from the lesson". The inspectors said planning for development of pupils' key skills was not consistent across the school and the head does not have enough involvement in determining the school's budget, restricting her ability to plan effectively.
The school also failed to meet some requirements on attendance and anti-bullying policies. Estyn recommended the school raises standards in IT and sets up arrangements to appraise and improve staff performance. It also suggested a strengthening of the role of the headteacher in leading and managing the school.
In a statement, the school said: "Having been the first independent primary school to be inspected under the new Estyn framework, the trustees welcome this report. Work has already been done on some of the recommendations."