Teachers should make more use of the skills and experiences of grandparents as working parents struggle to get involved in education, inspectors say.
Ofsted says grandparents have much to offer
In a survey of 25 schools, Ofsted inspectors found grandparents had a "positive influence" on pupils' behaviour, motivation and achievement.
The schools surveyed said they wanted more advice on how to involve parents, grandparents and carers in school life.
The findings follow concern that long working hours jeopardise family life.
The Ofsted report - Parents, carers and schools - found parents and carers who actively helped in school developed a better understanding of how pupils learned and how they could help their child.
But inspectors found many parents did not get the information they needed about how to help their children.
They found schools which encouraged parents to stay at school for the first 10 minutes of lessons saw the most success.
The report encourages schools to identify areas which would benefit most from input from parents and other carers and to involve them in setting school targets.
Grandparents were highlighted as one particular group with much to offer.
The report said: "Schools which actively encouraged the involvement of grandparents and other members of the extended family noticed significant improvements in children's attitudes and achievement.
"We recommend that schools seek to tap this important source of support."
The inspectors said the contribution of grandparents in schools where they were actively involved was valued by teachers.
"They also recognised the importance of extended family in a community in which an increasing number of parents and carers found it difficult to come to school because of work commitments and the demands of younger children.
"As well as contributing directly to the curriculum, in history for example, grandparents had a positive influence on pupils' behaviour, motivation and achievement.
"This was particularly noticeable in one school in which grandparents were learning about modern technology and helping the children with literacy."
Chief inspector Christine Gilbert said: "Parents and carers need more guidance about how they can support their children's learning.
"Schools should identify parents' and carers' special skills and interests, and find ways that they can be used to help learning. They should also involve the extended family, where possible."