What works? Evidence for decision makers

The Cabinet Office has published What works? Evidence for Decision Makers, a report that details the progress of the new What Works centres, which cover education, early intervention, policing and more.

I'm not going to analyse the report in detail, because mostly it's a collation of existing material. However, like many of these collations, sometimes something gets lost in the editing process. The section on education (about the work of the Education Endowment Foundation) includes a short paragraph on the use of teaching assistants as tutors. Says the first sentence:

Small group tuition can be a cost-effective alternative to one-to-one tuition as a way to provide intensive support for struggling pupils.

But it's the second sentence that had me scratching my head.

This is true despite the fact that small group tuition is on average, slightly  less effective than one-to-one tuition, because it is also much less expensive.

I think I know what they meant to say, but I've read it several times and still can't make sense of it.