\documentclass[a4paper]{scrartcl}
\usepackage[utf8]{inputenc}         % this is needed for umlauts
\usepackage[ngerman]{babel}         % this is needed for umlauts
\usepackage[T1]{fontenc}            % needed for right umlaut output in pdf
\usepackage[ngerman, num]{isodate}  % get DD.MM.YYYY dates
\usepackage{amsmath}

% See http://en.wikibooks.org/wiki/LaTeX/Footnotes_and_Margin_Notes#Margin_Notes
\usepackage{marginnote}             % write notes in margin
\usepackage[top=2.5cm, bottom=1cm, outer=3.0cm, inner=1.5cm, heightrounded, marginparwidth=1cm, marginparsep=0.5cm]{geometry}

\usepackage{enumerate}
\usepackage{minted} % needed for the inclusion of source code
\usepackage{lastpage}

\newcommand{\Student}{Martin Thoma}
\newcommand{\Matrikelnummer}{1634567}
\newcommand{\Nr}{1}

\pagestyle{empty}

\usepackage{fancyhdr}
\pagestyle{fancy}
\lhead{\Student}
\chead{Seite \thepage\ von \pageref{LastPage}}
\rhead{Matrikelnummer: \Matrikelnummer}

\usepackage{lipsum}

\begin{document}
\begin{center} \Huge{Übungsblatt \Nr} \end{center}

\section*{Aufgabe 1}
\lipsum[1]

\marginnote{\underline{$\;\;\;\;\;\;\;\;\;\;\;\;$} \\ Punkte}[0cm]


\section*{Aufgabe 2}
\lipsum[2]

\marginnote{\underline{$\;\;\;\;\;\;\;\;\;\;\;\;$} \\ Punkte}[0cm]

\section*{Aufgabe 3}
\lipsum[2]

\marginnote{\underline{$\;\;\;\;\;\;\;\;\;\;\;\;$} \\ Punkte}[0cm]

\marginnote{\underline{$\Sigma \;\;\;\;\;\;\;\;\;\;\;\;$} \\ Punkte}[2cm]

\end{document}