The figures from local authority meal providers around Scotland have been compiled by ASSIST FM.
Of the meals served, 75% of them are cold, with 60% of schools that contributed figures to the data serving only a cold meal option initially.
Among pupils entitled to Free School Meals, uptake is down only 20% compared to pre-Covid levels.
Jayne Jones, chair of ASSIST FM said: "Caterers across Scotland are working incredibly hard to deliver good food to pupils in schools at a time when they most need them.
“They have adapted delivery methods and menus to make sure our pupils still receive their lunch, with many offering pre ordering and cashless payments to help parents and pupils at this time.
"It is disappointing to see that uptake has dropped during the first full week back at school, we know some parents may be opting to send in packed lunches, or pupils in Secondary schools may be keen to leave the school building, especially as they perhaps have seen their friends for a long time. But research still shows that most packed lunches aren't always the healthiest option.
"We'd like to reassure parents and teaching staff that school meals are safe, they are the best way of making sure that our children and young people are properly fuelled for a day of learning in school - and our staff are ready and waiting to serve them tasty, nutritious and sustainable school meals each and every day."
LACA, the school meals organistion, has promised to undertake a similar exercise as schools in England return today (September 1st) as part of a joint initiative to provide a truly national picture.
In a statement, it said: “LACA are pleased to take part in this joint initiative with ASSIST to provide a snapshot of the school meal service as children return to school.
“We hope that these figures will be useful for suppliers and school managers alike. We will be publishing additional figures for England during the week of the 7th September.
“We encourage schools to provide hot meals for children wherever possible, we know that a hot school lunch provides the main meal of the day for many vulnerable children who may have missed out on this during the Covid-19 pandemic and the school holiday periods”