Schools in Grantham and Sleaford are the latest to confirm cases of coronavirus, plus a suspected but unconfirmed case in Skegness.
On Friday, Lincolnshire County Council had a list of 15 schools with cases of COVID-19.
Since then, two people from Gonerby Hill Foot Primary School in Grantham have tested positive for coronavirus, according to Grantham Journal.
Youngsters in a class bubble of Reception and Year 1 children, and another of children in Years 5 and 6, were told to self-isolate for 14 days. The two cases are not connected to each other.
Letters were also sent to parents of children at Kesteven and Sleaford High School last week after a Year 8 student tested positive for COVID-19, according to the Sleaford Standard.
Over 100 pupils must stay at home after all Year 8 students were told to self-isolate for seven days.
Seathorne Primary Academy in Skegness, which is part of the Greenwood Academies Trust, has closed its Year 4 classes from Monday, September 21 for a week.
A spokesperson for the Academy said: “The health, safety and wellbeing of our pupils and staff is our absolute priority. As an Academy, we take our duty of care extremely seriously and every decision is made with the best interests of our entire school community in mind.
“As a result of staff shortages arising from precautionary self-isolation measures, we have taken the decision to close two of our Year 4 classes for one week.
“We appreciate this may be a challenging time for the affected families and we will continue to be in regular contact with our pupils, parents and staff to facilitate remote learning and provide reassurance and up-to-date information.
“We also encourage anyone with concerns to contact the Academy directly so that we can provide the necessary support.”
Meanwhile, North East Lincolnshire Council has reported five cases, which is an increase of one from last week, and there is at least one case in North Lincolnshire.