Launching its first Scottish policy document, Marjory O'Donnell, the campaign's director, said parents still complained that schools were following out-of-date guidelines in preventing pupils from keeping their own medicine.
Around 120,000 school-age children, one in seven, suffer from asthma. One in five 12 to 14-year-olds are said to be affected and the problem is growing.
Ms O'Donnell said lack of direction from the Scottish Office and councils led to "misguided" practice in schools. Some teachers did not allow pupils to retain inhalers, keeping them in the class for safety or holding them centrally.
"There are fears in some schools that medicines may fall into the wrong hands. But we think the risk of that is outweighed by the risk of not being able to get your hands immediately on inhalers. The reliever inhaler opens up the airways and allows the child to breathe," she said.
Only a small number of pupils had severe asthma attacks in school. "It does not have to be a scary monster but we should not forget that asthma can be fatal," Ms O'Donnell said.
She believes pupils from the age of seven - and some even younger - should be allowed to carry their inhaler to relieve attacks. "The medicine has to go into the child and the easiest thing is if the child has it on them. Immediate action is vital," she said.
Research into asthma shows persistent difficulties related to an illness that affects tubes in and out of the lungs. Symptoms include coughing, wheezing, tight chest and shortness of breath. One in five pupils is diagnosed with asthma but some get better and others do not need continuous treatment.
Ms O'Donnell said some had difficulty sleeping and may turn up tired at school. A recent survey had shown that one in three sufferers lost three to four weeks of lessons the previous year.
The campaign is pressing the Scottish Office to issue fresh guidance on coping with asthma and urging local authorities to update their advice.
Leader, page 16
* A free schools pack - one per school - is available from the National Asthma Campaign Scotland, 21 Coates Crescent, Edinburgh EH3 7AF (0131 226 2544).