In a speech at St Mary's University in Twickenham, southwest London, Justine Greening set out her vision for a new model of grammar schools which is "truly open for all" and "working for everyone".
Her comments came as a Government consultation found that families excluded from traditional measures of deprivation but with a household income below the national average find it harder to get into outstanding schools.
This also means children in these households do not do as well as their wealthier peers.
The Education Secretary urged grammar schools to change their policies and admit more children from disadvantaged families - describing greater diversity as vital.
Ms Greening said: "The new schools that we will create will support young people from every background, not just the privileged few.
"Young people on free school meals - and those and those eligible for pupil premium. Young people from ordinary families that are struggling to get by."
Children in grammar schools are as likely to be from ordinary working families as children in non-selective schools, according to the Department for Education.
The department defines "ordinary working families" as those on modest incomes who tend to live outside the inner cities - including in suburbs and coastal areas.
Ms Greening said she wants to "knit together" different parts of the education system in a bid to raise attainment - as she believes universities, independent schools, and faith schools have a role in creating "better options for parents".
She added: "I believe that selection - in new, 21st century state grammar schools - will add to the options available to young people - to truly help make the most of their talents."
Labour leader Jeremy Corbyn has dismissed the plans for new grammar schools as "divisive".
On Twitter, he said the Conservatives should scrap the policy and provide more funding for current schools to help children from all backgrounds.
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