But the commissioners rejected his plea to support the removal of compulsion and decided to await the report of the Scottish Executive's working group on observance. This was set up after HMI reported that two out of three secondary schools did not meet the minimum recommendation of observance at least once a month.
Mr Hilsley, a Leith minister, described existing legislation as "a glorious muddle". He told The TES Scotland: "Religious observance falls into a vacuum of nothingness. I would like the Church to look at it objectively. Does it have any integrity at all? The Church has to look at what it has become in the context of a plural society and we have to look at what we are supporting."
The Kirk presently backed compulsory observance without examining the reality in schools, Mr Hilsley said, and local authority guidance differed widely. But the Rev Jack Laidlaw, education convener, replied that the terms of reference of the working group were to work within the law. It was likely to recommend a new circular of advice based on good practice.
In his own set-piece address, Mr Laidlaw referred back to the Millar committee's report on moral and religious education 30 years ago and its questioning of the place of observance in a multicultural society.
Mr Laidlaw said: "Worship in the context of the local church, where people gather because they want to be there and share values, beliefs and commitments before God, is quite different to religious observance in the local school where pupils and teachers may come from different faith backgrounds or from none."
Mr Laidlaw reported that more than a quarter of primary schools in Scotland and a third of secondaries had not shared with school chaplains clear ideas about observance and chaplaincy.
Anne Wilson, education director in Dundee, who chairs the Executive's working group, told The TES Scotland that the group had come up with a new definition of religious observance which would be posted on a website to be opened next month. This will form part of the basis of public consultation with a series of meetings beginning in Dundee on June 24.
The working group is charged with reviewing the current guidance which stipulates that assemblies must be of a "broadly Christian character". It does not have the option of considering whether observance should be compulsory.