JSFiddle - React, Tailwind, and code Playground

HTML

<div style="padding-bottom:8px;display:block;" id="grade_level_set_1">
    <select name="select_grade_set_1" id="select_grade_set_1" class="required">
        <option value="">&lt; Grade &gt;</option>
        <option value="Pre-K">Pre-K</option>
        <option value="K">K</option>
        <option value="1st">1st</option>
        <option value="2nd">2nd</option>
        <option value="3rd">3rd</option>
        <option value="4th">4th</option>
        <option value="5th">5th</option>
        <option value="6th">6th</option>
        <option value="7th">7th</option>
        <option value="8th">8th</option>
        <option value="9th">9th</option>
        <option value="10th">10th</option>
        <option value="11th">11th</option>
        <option value="12th">12th</option>
    </select>
    &nbsp;&nbsp;&nbsp;Num of Students:
    <input type="text" class="textfield2 required" id="number_students_set_1" maxlength="4" name="number_students_set_1"/>
</div>

<div id="remove_set_3" style="display: inline;">&nbsp;( <a name="#" style="cursor:pointer; color:#788D19; font-size:10px; font-weight:bold;">remove</a> )</div>

CSS

.error {
    color: red;
    font-weight: bold;
}

JavaScript

_err = "";
_posted = false;
_add_more = 1;
_num_groups = 7;
_blur_check = false;


window.onload = function () {
$('#school_form-grades-list').change(

function () {

    var grades_ = parseFloat($('input#number_students_set_1').val());

    if (grades_ >= 10) {
        $('input#number_students_set_1').removeClass('error');
    } else if (grades_ <= 9) {
        $('input#number_students_set_1').addClass('error');
    } else {

    }

});
    
};

$(function(){
    $('#remove_set_3 a').click(function(){
        remove();
    });
})

function remove() {
    $("#grade_level_set_" + _add_more).hide('fast');
    $("#remove_set_" + _add_more).hide();
    $("#select_grade_set_" + _add_more).val('');
    $("#number_students_set_" + _add_more).val('');
    if (_add_more == _num_groups) {
        $("#bt_addGradeSet").fadeIn();
    }
    _add_more = _add_more - 1;
    i = _add_more;
    $("#remove_set_" + i).css('display', 'inline');
}