Three key standards for looking after people with dementia are only "adequate or less" at almost four out of 10 care homes, a report by inspectors revealed.
Overall the Care Inspectorate found that more than half of the 145 homes it examined were "performing at a good or better level in terms of meeting people's needs, rights and expectations".
But chief executive Karen Reid (pictured) said: "There remain improvements to be made in ensuring that quality of life for people is not limited due to lack of expectations of what it means to be an older person living with dementia in a care home."
When it comes to providing end of life care that respects an individual's wishes, inspectors said the performance of 42.1% of homes was adequate or lower.
Two fifths (40%) of homes received this grading when it came to ensuring residents have the right to be as independent as possible and to be included in the community.
When inspectors looked at whether carers were well supported and educated about dementia, 38.6% of homes were ranked as adequate or lower on this standard of care.
The report was based on studies of 145 care homes across Scotland between June 2016 and March 2017.
The inspectors said: "We found that over half of care homes were performing at a good or better level, however there remain improvements to be made in ensuring that quality of life for people is not limited due to lack of expectations of what it means to be an older person living with dementia in a care home."
Some 90,000 people across Scotland have been diagnosed with dementia, and a proportion of these people will live out their final years in care homes.
While 55% of homes at ongoing organised activities for residents every day of the week, 10% of homes did not provide any opportunities for people to keep active or engaged.
Although the majority of care homes now have secure gardens, the report found more than a third could not be accessed independently, with residents requiring a staff member to be present if they wanted to go into the garden.
And in 45% of care homes staffing levels frequently prevented people from going out into the community at least once a week.
Ms Reid said: "It is possible to live well with dementia, and care services play a crucial role in supporting people to do so.
"The evidence presented in today's report shows examples of excellent care being experienced by people living with dementia, across all parts of Scotland, as well as areas for development and improvement.
"For example, we found inconsistent and variable post-diagnostic support for people and their families, when someone in a care homes is diagnosed with dementia.
"While we recognise that the number of people receiving a diagnosis at this point in their life may be relatively low, we expect people living in care homes to have the same access to diagnostic and support services as people living in the community."
She added: "There are a small number of care homes where the quality of care was not satisfactory when we inspected.
"For those that are not providing the care and support that we would like to see, the Care Inspectorate requires speedy improvement and can provide direct support to ensure the quality of care improves.
"We are committed to ensuring that quality of life for people is not limited due to lack of expectations of what it means to be an older person living with dementia in a care home."
Mental Health Minister Maureen Watt said: "The Scottish Government welcomes the Care Inspectorate's important report on dementia care in care homes.
"It shows encouraging improvements in the quality of care provided, particularly in person-centred care. While examples of excellent care are demonstrated, there are also significant areas identified for improvement, such as more consistent post-diagnostic support in accordance with our national commitment and better end of life care.
"We continue to support implementation of the dementia care standards in care homes and all other care settings through our national support for the dementia skills framework Promoting Excellence.
"In addition, as part of our 2017-2020 National Dementia Strategy we are also working with partners to embed and improve access to post-diagnostic support and to significantly enhance palliative and end of life dementia care."
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