If approved the proposal could lead to shorter summer breaks for Swedish school pupils.
"It is alarming to see how school results are dropping and particularly reading skills, which is the basis for all other learning," Annika Eclund, head of the Christian Democrats schools policy group, told Sveriges Radio (SR).
A parliamentary inquiry has shown that the time allocated to Swedish language teaching has shrunk by 300 hours since the 1960s, from 1,800 hours to 1,500.
When it comes to literacy Swedish pupils are falling behind in international league tables.
According to the Sweden Democrats this has to do with a number of factors, including a shorter than average compulsory schooling compared to the rest of Europe.
Swedish pupils aged 9 to 11 study 50 hours less than the European average. In the 12 to 14 age group, Swedes study 130 hours less.
The Centre Party and the Liberal Party are positive to the proposal but the Moderate Party said they want to prioritize efforts to improve poor-performance schools and to get more skilled teachers.
The Swedish Teachers' Union also believes extending the school year is the wrong approach.
"All international research and experiences show that what really improves results is access to well-educated and competent teachers. That is what we need," Eva-Lis Sirén, chair of the Teachers' Union, told Sveriges Radio.
"We currently have unqualified teachers in Swedish school, but we also have a lack of teachers," she added.
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But Mattias Hallberg, chair of Sweden's Student Associations (Sveriges elevkårer) thinks that pupils would actually welcome more Swedish classes, but he is not sure shortening the summer break is the right way forward.
"I think you could do a lot when it comes to improving scheduling, such as fewer free periods during school days," said Hallberg.
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