Hello @jay2jam. You can use your code to achieve that. Try this, let me know if it works.

<template>
    <div>
        <mdb-dropdown>
            <mdb-dropdown-toggle slot="toggle" size="lg" outline="primary" darkWaves>
                {{subjects[currentIndex]}}
            </mdb-dropdown-toggle>
            <mdb-dropdown-menu color="primary">
                <mdb-dropdown-item v-for="(sub, i) in subjects" :key="i" @click.native="pickSubject(i)" :active="i ===
            currentIndex">{{sub}}
                </mdb-dropdown-item>
            </mdb-dropdown-menu>
        </mdb-dropdown>
    </div>
</template>

<script>
    import {
        mdbDropdown,
        mdbDropdownItem,
        mdbDropdownMenu,
        mdbDropdownToggle
    } from 'mdbvue';

    export default {
        name: 'App',
        components: {
            mdbDropdown,
            mdbDropdownItem,
            mdbDropdownMenu,
            mdbDropdownToggle
        },
        data() {
            return {
                currentIndex: 0,
                subjects: ['Science', 'History', 'English']
            };
        },
        methods: {
            pickSubject(i) {
                this.currentIndex = i;
            }
        }
    };
</script>