I want to know if Christian schools in the UK help children find faith
in God.   What sort of schools are most effective in this regard?  The
expert on this is Leslie J. Francis from the University of Wales in
Bangor but the most recent review article I can find seems to be from
1994 and mostly talks about primary schools (ie up to age 11).  Is
there anything more recent and can we say anything about secondary
schooling? Or private Christian schools?

Most of the larger Christian schools in the UK are run under the
auspices of either the Anglican or Roman Catholic churches with other
Christian denominations supporting many of the smaller schools (often
with a relative handful of pupils).

Entrance to the larger schools particularly is often highly
competitive as they tend to produce above average results among their
pupils. Whilst the entry criteria for these schools favours those
coming from their own Christian tradition they do accept entrants from
other traditions, from other faiths and from no faith. Typically
applicants for places will have to obtain a reference from their
priest, vicar or pastor supporting their application. The smaller
schools sometimes specialise in pupils with particular educational
needs and are often excluded from the Government's "league tables" as
a result.

As most of the pupils of these schools will inevitably come from
Christian families I suspect it would be difficult to determine the
direct impact of the school environment on their coming to faith.

There are a number of references to studies which may further help you
in your research

http://www.nfer.ac.uk/htmldocs/Outcome_ISP.doc

http://www.guardian.co.uk/religion/Story/0,2763,593030,00.html

http://www.lynnejones.org.uk/faith.htm

http://www.methodist.org.uk/information/02schools.htm

http://www.glos.ac.uk/humanities/content.asp?pid=23

http://www.christianschoolstrust.co.uk/intro.htm