Range filter proto

Screener.js

var stream = m.stream
var levels = {
  5: 'Daycare or Kindergarten',
  12: 'Primary',
  16: 'Secondary',
  18: 'Senior Secondary'
};

var App = {
    age: stream(0),
    oninit: function (vnode) {
      vnode.state.level= vnode.state.age.map(function (ag) {
        if (ag > 18) return 'out of school';
        var index = Object.keys(levels).filter(function (lev) {return ag < Number(lev);})
        console.log(levels[index[0]])
        return ag && 'in ' + levels[index[0]];
      })
    },
  view: function (vnode) {
    return [
      m('h3', 'School kids app'),
      m('p', 'How old is your kid?'),
      m('input', {
        value: vnode.state.age(),
        oninput: m.withAttr('value', vnode.state.age)      
      }),
      m('h5', vnode.state.age()? 'Your kid is '+ vnode.state.age() +' and most likely ' + vnode.state.level() : '')
      
    ]
  }
}

m.mount(document.body, App)

Demo here

@JAForbes suggestions 1 and 2

@barneycarroll suggestion here