Advice to recruitment agency - candidates coming from recruiting agency are unable to clear the test

We are a corporate company and before we hire a candidate - they have to clear some test. Unfortunately the candidates coming from recruiting agency are unable to clear the test.
The agency is asking for advice from me.
Pls help me draft an email to the recruitment agency.
FYI test is only way we can hire the candidate.
Looking for a revert on the same soon.

Dear member,
Conducting recruitment tests related to the job is a good hiring practice. Nevertheless, if the candidates get filtered out in the recruitment tests then it shows that the candidates were not worthy. Your concern is that administering the recruitment tests is a time-consuming activity. If the candidate fails then it wastes your as well as recruitment agency's time.
Against this backdrop the following questions arise is what kind of these tests are? Are these aptitude tests or tests related to the work? If latter then nothing wrong if the candidates are filtered out. It is common practice in each industry.
While academic score may not show candidate's real talent, can the recruitment tests be related to any academic subject? If yes, then you may fix a level of minimum marks scored in that subject. It could be ≥ 65% or even more
If the candidates' are failing in aptitude tests, then fix the minimum academic score for graduation at ≥ 65%
I have seen in the recruitment of the IT companies engineering candidates' failing in the aptitude tests. But then it is common. Out of 10 barely one candidates reaches to the level. Possibly in this method the recruitment may become costly but then cost of wrong hire is far greater than the cost of the unit recruitment.
Thanks,
Dinesh Divekar

Dear Anon,
Since you are recruiting from outside agencies, can it be assumed that they are empanelled with your company? If so it would be prudent to inform them of the type of tests you subject the candidates to so that the recruiting agency can itself brief the candidates while shortlisting.
Your mail to them should contain a brief about the tests and also a proper brief about the designation for which the candidate is being considered.
Hope this helps.
Regards,
R H Kavarana
HR Manager

Dear Anon,
As has been rightly pointed out your post indicates that there is a recruitment firm retained by your organization. If this be so I suggest your mail should give an idea to the recruiting firm of the JD of the prospective employees, the set of competencies-skills-education credentials required with prospective candidates as would also be dictated by the JD .
This would enable the recruitment agency to filter a panel of close fit candidates who are quite likely to pass your test. As a desperate measure, last resort, you may share the pattern of your test, may be an older version, with the recruitment firm.