The Department for Education and Skills has increased its spending on private consultants from pound;5 million to pound;22 million in three years, without considering using its own staff.
In a damning report, the National Audit Office, the public sector watchdog, also revealed that a quarter of the department's consultancy contracts have been awarded without being put out to tender.
The department was told by the Parliamentary Public Accounts Committee in 2002 that this practice should be reduced. But the DfES has continued to allow its managers to award contracts worth up to pound;250,000 without specialist advice or competitive tendering.
Spending on consultants by the department has shot from pound;5 million in 200304 to pound;9 million in 200405 and to pound;22 million in 200506, according to the auditors. And the department has failed to assess how work should be divided between consultants, who can earn between pound;300 and pound;1,000 for a single day's work, and its own civil servants.
"There is little evidence that internal expertise is considered first," the report says. "The internal staffing route is rarely used, partly because the department does not hold adequate information on skill and availability of staff."
The audit office put the department bottom of the class among the five Whitehall departments it investigated over the use of consultants.
A DfES spokesman dismissed the study as "narrow and limited".
The verdict came as a second report from the watchdog gave the DfES the wooden spoon - this time out of six departments - for its inability to monitor its own performance against targets set by the Treasury. This included checking progress on numeracy and literacy targets, GCSE results narrowing the achievement gap for children in care, school attendance and pupil participation in PE and sport.
The watchdog found three out of 17Jtarget monitoring systems were "not fit for purpose", while another 12 needed strengthening.
A DfES spokesman said it had already agreed to review systems.