Here is my best attempt at collecting the evidence requested.
OP has stated under David Ebert's answer that they would be happy with formative assessments being returned. However, many of the objections to returning assessments are with summative assessments (reduced cheating, "reduced variability"...). The point of formative assessment is not reliable measurement, but increased achievement.
There is empirical data on the benefits of well managed formative assessment in partnership with students ("achievement gains of one-half to two standard deviations" see below). Part of this is "continuous access" to the information, which I take to be the intent of the OP.
An easy to understand explanation of formative assessment:
Margaret Heritage explains how formative assessment is carried out by teachers (tests and informal activities) and students (peer and self evaluation), and used by teachers (to improve teaching) and students (to guide their own learning).
Some principals of formative assessment:
"First, whatever method teachers use to elicit evidence of learning, it should yield information that is actionable by them and their students." "...students can take active steps to advance their own learning."
From all the above we can see that formative assessment is not solely created by or for the sole use of the teacher.
Rick Stiggins (below) explains that formative assessment is created in partnership with students, and with students having "continuous access" to the information.
A widely referenced paper is:
Rick Stiggins, From Formative Assessment to Assessment FOR Learning: A Path to Success in Standards-Based Schools, Phi Delta Kappan, Vol. 87, No. 04, December 2005, pp. 324-328.
"Assessment FOR learning rests on the understanding that students are data-based instructional decision makers too."
Students "must have continuous access to evidence of what they believe to be credible academic success, however small."
"Students partner with their teacher to continuously monitor their current level of attainment in relation to agreed-upon expectations so they can set goals for what to learn next and thus play a role in managing their own progress. Students play a special role in communicating evidence... to their families... "
"When consistently carried out as a matter of routine within and across classrooms, this [Assessment for Learning] has been linked to achievement gains of one-half to two standard deviations on high-stakes tests, and the largest gains made are by low achievers."
The thrust of the article is that as long as teachers see formative assessment as something that is owned by the teachers and primarily for use of the teachers, they are really missing the point of formative assessment.
From further reading, it is clear that it is the board - the institution - that is seeking ownership rights. Many teachers have apparently stated that they disagree with the boards position. Legal opinion also disagrees, and most commentators make it clear that society as a whole disagrees.
So, from a property perspective it is acknowledged that students are the owners of the material that they create while they are learning, unless it is produced under "work-for-hire", or the ownership has been explicitly signed over to the institution. The refusal to hand over material that has been created by students and is requested by those students, in absence of substantial overriding concerns (a necessary embargo period on the return of summative assessments) is a breach of property rights.
One university gets around this by including this clause:
When a student submits work as a course requirement, the student retains ownership of the work, but ownership of the physical or electronic document shall be vested in the College. The College is granted a perpetual, royalty-free license by the submitting student to make copies of the work for administrative and educational purposes.
So the university can hold on to coursework, as the physical document belongs to them. However it is clear that the university has no intention of permanently disallowing students from having access to material that they have produced. Allowing students to have a copy for themselves is necessary for them to practice their ownership of copyright.
Several answers indicate that their personal preference is for students to have full access to tests, while departmental policies prohibit this. Like any institution, schools seek to keep as much information as possible internal to the organisation. This increases the power of the institution - which is not necessarily a bad thing, as empowered teachers can help students.
The fundamental error comes from the institutional (not personal) perspective that students are primarily an object that is taught, so an empowered teacher is more important to success than an empowered learner. It is this institutional attitude that is probably more damaging for student achievement than any particular policy on whether or not students have access to formative assessments.