After the In Work tax credit came in the gap between being on a benefit and working for the minimum wage opened up.
This has undoubtedly contributed to the fall in the number of benefit-dependent sole parents. But anti-child poverty activists want the in work tax credit paid to all beneficiaries. This will be a sticky issue for the new government. Their families package (especially the payment for babies aged 0-2) will effectively close the gap anyway.
Another interesting fact from the Briefing. Maori represent 15% of the population but "48 percent of Sole Parent Support recipients."
Here's a table from my own 2008 paper, Maori and Welfare:
It would appear the employment status of Maori sole parents is not improving as quickly as the general population.
A question remains that I have not had time to properly research. While the number of sole parent support recipients continues to drop...
... it must be remembered that many are now moved onto jobseeker support as their youngest child reaches 14. There may also be some migration onto the supported living benefit positively affecting the drop. The Briefing stresses that "The proportion of clients with mental health conditions has been growing substantially over time."