However, all visitors to the school will be required to wear a mask. Masks for both students and staff on-site is optional.
"We've kept it really simple - our school is essentially a whānau bubble. Our main things are constant sanitising and keeping awareness of the distance between us," he said.
"We've found over the last week with the level 3 kids on-site is that most have fairly good awareness anyway. It's about praise and prompt, rather than being punitive."
Johnston said he was expecting most of the students to show up for classes, but accepted there was a degree of "Covid anxiety" among families.
"I don't know what the numbers will be, but there will be some. Previously, it's been around 4 to 5 per cent. There will be a small group."
It's a similar story at Whanganui Intermediate School, with the school expecting most students to show up.
"Last time we had a lot of students stay out at level 2, but I don't think we're going to have as many out this time. We've been in and out of level 2 a few times over the year," principal Kathy Ellery said.
"It's looking really positive actually, I'm confident we'll have most of our kids back. It won't be the same as the previous nationwide lockdown."
Ellery said general common-sense level 2 guidelines would be applied at the school, such as no assemblies for the duration of the restrictions, and postponing the school cross country until the end of the school term.
"We're still classed as a primary school, so while children and staff are welcome to wear masks if they want to, it's not mandated as necessary.
"Ventilation is the biggest thing - we have to make sure classrooms are well ventilated between classes."
Whanganui High School is also opening up with principal Martin McAllen telling the school community on Tuesday that staff were ready to welcome students back.
"It is wonderful news that all students in our region will be able to return to school on Thursday – under full alert level 2 conditions and expectations," McAllen said in a statement.
"Students and staff will be looking forward to seeing one another again and it will be great for face-to-face learning and teaching to be able to resume so quickly after a reasonably brief period of distance learning."
Unlike primary schools, there was an official recommendation for students and staff at high schools to wear a face covering, but it is not a requirement.
For senior students, the lockdown restrictions mean in-school senior examinations have been pushed back to the end of this term.
UCOL's Whanganui campus is also set to reopen under alert level 2, but that isn't scheduled until Monday.
UCOL's health and safety manager Sylvie Hickton said the delay in opening was to ensure the campus had all necessary health precautions in place to keep students safe.
"These preparations are about making sure our campus is safe and welcoming, with clear signage, hand sanitiser stations, and more cleaning of high-touch areas.
"Where we need to we'll be changing our classroom layouts to ensure physical distancing, and scanning the Covid app will be required."
Hickton said she expected most students would return on Monday.